Leonardo Mayer of Argentina upset top-seeded Philipp Kohlschreiber 6-4, 7-6 (7/4) to reach the quarter-finals of the Bet-at-Home Cup on Tuesday.
Mayer converted the only break point of the opening set and saved two set points for the 26th-ranked German in the second, before wrapping up the victory with a service winner in the tiebreaker.
“It was a bad match, I just couldn’t find my usual game,” last year’s finalist Kohlschreiber said. “I didn’t start well and was lacking confidence in my strokes.”
The 78th-ranked Mayer, who also beat Kohlschreiber in straight sets in their only previous meeting at Roland Garros last year, will next play Marcel Granollers of Spain.
The game will be Mayer’s second quarter-final of the season after he lost to Rafael Nadal in the last eight in Acapulco, Mexico, in February.
The eighth-seeded Granollers led Horacio Zeballos 6-0, 2-0 when the Argentine pulled out injured. Granollers, who conceded only one point on serve, also reached the quarter-finals in Gstaad, Switzerland, last week.
Earlier on Tuesday, two-time champion Robin Haase started his title defense by defeating Guillaume Rufin of France 6-4, 7-6 (7/4) in the first round.
The 68th-ranked Dutchman was a break up in the second set, but lost his lead before converting his second match point in the tiebreaker. He finished with 10 aces.
Haase, who won the event in 2011 and last year and reached his third career final in Gstaad, Switzerland, last weekend, will next play Daniel Brands.
The German beat fifth-seeded Carlos Berlocq of Argentina 7-6 (7/4), 2-6, 6-2.
Andreas Haider-Maurer saw off Dennis Novak 6-4, 6-4 in an all-Austrian tie; Guillermo Garcia-Lopez of Spain rallied to beat Thomaz Bellucci of Brazil 6-7 (1/7), 6-3, 7-6 (7/4); Victor Hanescu of Romania defeated Aljaz Bedene of Slovenia 6-2, 6-1; and Jan Hajek of the Czech Republic ousted Aldin Setkic of Bosnia by the same score.